Who qualifies for promotion among the following options?

The qualification for promotion is often determined by a combination of time in grade, time in service, and performance evaluations, such as proficiency and conduct marks. In this case, the correct choice highlights a lance corporal with 12 months time in grade and 21 months in service, which meets established requirements for promotions within the ranks.

Time in grade typically serves as a foundational requirement, indicating that the individual has adequately served in their current position to demonstrate leadership potential and capability. Additionally, having 21 months in service reflects a level of experience that is generally valued when considering promotion, as it indicates a commitment to the organization and exposure to various duties and responsibilities.

In summary, a lance corporal meeting both the time in grade and time in service criteria is well-positioned for promotion, as it suggests readiness to take on additional responsibilities associated with the next rank.